1. Field of the invention
The invention relates to a laser cutting method using an ytterbium-based fiber laser source.
1. Related Art
Laser cutting using a CO2 laser source for generating a laser beam with a wavelength of 10.6 μm, with a power ranging up to 6 kW at the present time, is widely used in the industry as this type of source gives good beam characteristics, namely a good quality factor (M2, BPP, etc.) and a good spatial energy distribution (TEM01*).
It is possible with these CO2 laser sources to cut metals and their alloys, such as aluminum and its alloys, stainless steel, carbon steel, mild steel, etc., or any other nonmetallic material, such as wood, board, ceramics.
However, the cutting speeds that can be achieved and the cutting quality that results therefrom are highly variable, depending on the material to be cut and, moreover, depending on the cutting method parameters adopted, such as the nature of the assist gas, the diameter of the focused beam and the power of the incident laser. In addition, the optical path must necessarily be maintained in an inert atmosphere so as to avoid any contamination and to preserve a medium of constant optical index necessary for good propagation of the beam.
In an attempt to alleviate these problems, it has been proposed to use in laser cutting Nd:YAG laser devices. In this case, the resonator that generates the beam contains a solid-state amplifying medium, which is a neodymium (Nd) rod, and the beam thus obtained is then sent via a optical fiber to the focusing head.
However, this solution is not satisfactory from the industrial standpoint as it gives poor results in terms of cutting quality and cutting speed, not only because of beam quality factors (BPP) unsuitable for laser cutting but also because the transverse energy distribution in the beam is not Gaussian but has a top-hat profile, while beyond the focal point the transverse energy distribution is even random.
The problem that arises is therefore how to provide an improved laser cutting method, which does not have the abovementioned drawbacks and limitations and can achieve, depending on the thickness in question, speeds ranging up to 15 to 20 m/min, or even higher, and good cutting quality, that is to say straight cutting faces, with no burrs and limited roughness.